1. Field of the Invention
The present invention relates to a latent image forming method to form a background and latent image with surface brilliance difference of the surface of an overcoat layer in the event of layering an overcoat layer onto an image with a thermo-sensitive transfer method (thermal transfer method), a printer device to which this latent image forming method is applied, a visualizing method to visualize the latent image as a line moiré by observing the latent image through a visualizing tool having lines of similar pitch as the above-mentioned lines, and a visualizing tool employed for the visualizing method.
2. Description of the Related Art
With a technique according to related art, a visualizing method forms a line pattern by printing, an image which is targeted as a latent image is hidden therein, and a visualizing tool having a line pattern with a similar pitch is provided as a transparent substrate (e.g. see Japanese Unexamined Patent Application Publication No. 53-028443 and Japanese Unexamined Patent Application Publication No. 2005-043778). These techniques are employed primarily for (1) authenticity determination of stocks and bonds (predetermined information is embedded as a latent image in the same image) and (2) authenticity determination of a document copy and an original document (a phenomenon that the lines may not be accurately reproduced in the event of a copy is used) and so forth. However, in order to hide the latent image within the image, the latent image portion and the background portion thereof should be images having roughly similar high uniformity in density, and design constraints have also occurred, causing difficulty in applying to a full-color image such as a photograph.
Also, a method to determine the authenticity by similarly employing moiré with a digital printer is disclosed in Japanese Unexamined Patent Application Publication No. 2000-280663 and Japanese Unexamined Patent Application Publication No. 2001-144944. With both the Japanese Unexamined Patent Application Publication No. 2000-280663 and Japanese Unexamined Patent Application Publication No. 2001-144944, a background and latent image are made up of lines or halftone dots, and the latent image is visualized by employing a visualizing tool whereby a moiré pattern appears, but design constraints have also occurred. With the Japanese Unexamined Patent Application Publication No. 2000-280663 a dye sublimation thermal transfer method is employed, but a determining region with moiré is provided separate from the photograph image.
In recent years, as various types of data have become electronic and information has become digitized, various techniques have been considered for electronic signatures or digital watermarking wherein information relating to copyright and other attribute information is added as invisible information to digital information. One example of such a technique is a method called an image deep layer signal. This technique embeds added information into primary image information as invisible information, and is effective in preventing replicating or tampering of image information having a copyright such as photographs, or securities and various types of cash vouchers.